The invention relates to a new and improved process for preparing bridged stereorigid metallocenes via organomagnesium and organotin compounds.
Metallocenes based on cyclopentadiene, indene and fluorene are, in combination with specific cocatalysts such as, for example, aluminoxanes or tetraphenylborate complexes, highly active catalysts and with suitable ligand systems also form stereospecific catalyst systems for the polymerization of olefins.
These catalysts, processes for their preparation and their use are described in detail in EP-A-0 480 390, EP-A-0 413 326, EP-A-0 530 908, EP-A-0 344 887, EP-A 420 436, EP-A-0 416 815, and EP-A-0 520 732.
The compounds specified therein are largely produced in accordance with the reaction scheme given, for example, in EP-A-0 480 390, page 5. In this method, the cyclopentadienyl derivatives are metallated with lithium alkyls, subsequently reacted with alkyl dihalides or alkyl ditosylates to give the bridged ligand systems and then, in a subsequent step, reacted again with lithium alkyls to give the corresponding dimetallated compounds which then react with transition metal halides to give the bridged metallocenes (J. Organomet. Chem., 1985, 288, 63; J. Organomet. Chem., 1988, 342, 21).
These processes have a series of disadvantages:
multistage syntheses in which the intermediates sometimes have to be isolated and purified,
it is necessary to carry out individual reaction steps at temperatures .ltoreq.56.degree. C.,
use of solvents which are not unproblematical in terms of safety and/or environmental considerations, such as ether, hexamethylphosphoramide (HMPA), methylene chloride or chloroform,
separation processes (e.g. extractions), particularly in the last step, which in combination with the material properties of the products (sparing solubility, extreme sensitivity to traces of air and moisture) and the salts to be separated off (e.g. LiCl) can only be carried out industrially at high cost and contribute to high losses in yield,
control of the rac:meso ratio during the synthesis in the case of compounds which, owing to the ligand substitution, can in principle be formed in a racemate (rac) (two enantiomers) and a meso form, is not generally possible (hitherto the formation of the meso compound could be reduced or prevented only by working at -56.degree. C. in a few individual cases),
only small yields of the desired metallocene, particularly when calculated over all steps.
Therefore there is increasing interest in the provision of suitable, general synthetic processes, particularly also those which can be used without problems for industrial amounts, which are able to give such transition metal complexes in high yields as cheaply as possible.
It is an object of the invention to derive synthetic processes which allow, while avoiding the indicated disadvantages, the preparation of bridged stereorigid metallocenes in high yields, as a matter of choice with or preferably without isolation of the intermediates, and can also be carried out industrially without problems.